This invention relates to a label reader of the class using a laser light beam and more particularly to a head construction for such label readers.
In discussing prior art, reference is had to FIG. 2 of the accompanying drawings which shows a typical example of the conventional laser beam label reader. As shown in FIG. 2, the head of the conventional reader has a fixed light receiving axis P and is therefore required to have a wide view angle Q to receive light signals from labels 20, 21 and 22. However, a head with a wide view angle is easily influenced by ambient light and has met difficulties in improving the S/N ratio. More particularly, if the sensitivity of a photomultiplier tube 23 is increased, it will be easily saturated with the ambient light and become incapable of picking up signal light. In this connection, it may occur to use various filters such as an ND filter and the like for the purpose of limiting the light amount. However, the use of such filters will contribute to attenuate the light signals as well. Even if an interference filter which passes only laser light is used, the ambient light contains components of the wavelength same as that of the signal light in a large quantity and therefore will drive the photoelectric multiplier also into the saturated range, making it utterly difficult to improve the S/N ratio.